This invention is related to a method and apparatus for estimating the slope of a surface on which a vehicle is operating, and for controlling the vehicle based on the estimated slope information.
Vehicles that are comfortable to ride in are in great demand in recent years. In order to satisfy such demand, it is necessary to provide smooth control of the automatic transmission and other systems in response to the operating conditions in which the vehicle is running, such as, for example, going up or down an incline.
It is of course easy to sense a slope using a slope meter if the vehicle is at rest. However, when the vehicle is running, it is almost impossible to sense the slope using such a slope meter because the slope determination can be affected by acceleration of the vehicle. Such slope meters are therefore not useful for the conventional arts to sense the slope on which the vehicle is running. Instead, known devices have been developed to judge the status of any slope based on information concerning the engine output.
As described in Japanese Patent Laid-Open No. 24362/1991, conventional slope estimation units have used vehicle speed, throttle opening, and the rate of change of throttle opening to determine the subject slope status, and have controlled shifting of the vehicle gears according to the slope. However, such conventional units cannot sense a slope accurately enough to assure a comfortable driving environment to the driver.
A different technique is used in Japanese Patent Laid-Open No. 70307/1985, in which the slope is calculated based on longitudinal vehicle acceleration sensed directly and the acceleration found by calculating the rate of change of the vehicle speed. In this method, a pulse output vehicle speed sensor is used, and the sensor output is converted to voltage signals in a frequency-voltage converter.
The accuracy of slope estimation may be affected by the status and mechanical characteristics of the engine in some cases. For example, errors are apt to occur when the throttle opening is changed abruptly, when the brakes are applied, while a gear is being shifted and in other transient situations.
In prior art devices, output shaft torque is calculated and the acceleration torque is determined from the differentiated vehicle speed. However, estimation errors seem to be unavoidable due to the mechanical characteristics of the engine and the transmitter.
In other prior art, an acceleration sensor is used to detect the acceleration in the longitudinal direction of the vehicle. When the vehicle is going up or down a hill, the acceleration due to gravity affects this sensor so that it is impossible to find the acceleration of the vehicle correctly. Moreover, the latter method mainly utilizes analog processing which includes a frequency-voltage converter. Problems also arise because the errors generated by large fluctuations in vehicle running speed are not taken into account. In addition, the hardware required for this method is very expensive.
The purpose of the present invention, therefore is to provide a slope estimation apparatus, which eliminates estimation errors by eliminating noises appropriately to the physical phenomena and mechanical characteristics of the engine and the transmission. The slope can thus be estimated accurately and the estimated slope information can be used to control the vehicle, such as for example the shifting pattern of an automatic transmission. In other words, the purpose of this invention is to supply a slope estimation unit that can output consistently highly accurate slope estimation information.